The viscosity of lubricating oils, particularly the viscosity of mineral oil based lubricating oils, is generally dependent upon temperature. As the temperature of the oil is increased, the viscosity usually decreases.
The function of a viscosity improver is to reduce the extent of the decrease in viscosity as the temperature is raised or to reduce the extent of the increase in viscosity as the temperature is lowered, or both. Thus, a viscosity improver ameliorates the change of viscosity of an oil containing it with changes in temperature. The fluidity characteristics of the oil are improved.
Numerous types of additives are used to improve lubricating oil and fuel compositions. Such additives include, but are certainly not limited to dispersants and detergents of the ashless and ash-containing variety, oxidation inhibitors, anti-wear additives, friction modifiers, and the like. Such materials are well known in the art and are described in many publications, for example, Smalheer, et al., "Lubricant Additives", Lezius-Hiles Co., Cleveland, Ohio, USA (1967); M. W. Ranney, Ed., "Lubricant Additives", Noyes Data Corp., Park Ridge, N.J., USA (1973); M. J. Satriana, Ed., "Synthetic Oils and Lubricant Additives, Advances since 1977", Noyes Data Corp., Park Ridge, N.J., USA (1982), W. C. Gergel, "Lubricant Additive Chemistry", Publication 694-320-65R1 of The Lubrizol Corp., Wickliffe, Ohio, USA (1994); and W. C. Gergel et al., "Lubrication Theory and Practice" Publication 794-320-59R3 of The Lubrizol Corp., Wickliffe, Ohio, USA (1994); and in numerous United States patents, for example, Chamberlin, III, U.S. Pat. No. 4,326,972, Schroeck et al., U.S. Pat. No. 4,904,401, Blystone et al., U.S. Pat. No. 5,356,546 and Ripple et al., U.S. Pat. No. 4,981,602. Many such additives are frequently derived from carboxylic reactants, for example, acids, esters, anhydrides, lactones, and others. Specific examples of commonly used carboxylic compounds used as intermediates for preparing lubricating oil additives include alky- and alkenyl substituted succinic acids and anhydrides, polyolefin substituted carboxylic acids, aromatic acids, such as salicylic acids, and others. Illustrative carboxylic compounds are described in Meinhardt et al., U.S. Pat. No. 4,234,435; Norman et al., U.S. Pat. No. 3,172,872; LeSuer et al., U.S. Pat. No. 3,454,607, and Rense, U.S. Pat. No. 3,215,707.
Dispersants are well-known in the lubricating art. Dispersants are employed in lubricants to keep impurities, particularly those formed during operation of mechanical devices such as internal combustion engines, automatic transmissions, etc. in suspension rather than allowing them to deposit as sludge or other deposits on the surfaces of lubricated parts.
Conventional dispersants are poor contributors to improving high temperature, e.g., 100.degree. C., viscosity. Mixtures of conventional dispersants with polymeric viscosity improvers are often used but such combinations are costly and may adversely affect low temperature viscometric performance.
Dispersant-viscosity improvers which provide both dispersancy and viscosity improving characteristics to an oil are well known.
It has now been found that mixtures of carboxylic compositions and derivatives thereof, as set forth in greater detail hereinbelow provide improved 100.degree. C. viscosity to lubricants without adversely affecting low temperature properties.